Study on long term reliability of photo-voltaic modules and analysis of power degradation using accelerated aging tests and electroluminescence technique

To improve PV module's lifetime and reliability, it is essential to understand the mechanisms and causes that degrade module performance over time under different climatic conditions. In this study, our main aim is to correlate the degradation of module power with physical changes that are generated in the cells over time. The poly-crystalline silicon 200W modules are subjected to long term accelerated tests (testing to be continued until failure occurs) and cell level defects are characterized using electroluminescence (EL) technique. The characterization is done periodically to analyze the trend of physical changes occurring in the module under aggravated stresses and degrading module's performance. Also, change in series resistance under thermal stress is analyzed as it has a direct impact on module's output power. Iterative simulation based software and EL images have been used to estimate series resistance of the cells.